Classification
There are more than 200 known Upanishads, one of which, the Muktikā, gives a list of 108 Upanishads – this number corresponding to the holy Hindu number of beads on a mala or Hindu rosary. Modern scholars recognize the first 10, 11, 12 or 13 Upanishads as principal or Mukhya Upanishads and the remainder as derived from this ancient canon. If an Upanishad has been commented upon or quoted by revered thinkers like Shankara, it is a Mukhya Upanishad, accepted as shruti by most Hindus.
The new Upanishads recorded in the Muktikā probably originated in southern India, and are grouped according to their subject as (Sāmānya) Vedānta (philosophical), Yoga, Sanyasa (of the life of renunciation), Vaishnava (dedicated to the god Vishnu), Shaiva (dedicated to Shiva) and Shakti (dedicated to the goddess). New Upanishads are often sectarian since sects have sought to legitimize their texts by claiming for them the status of Śruti.
Another way of classifying the Upanishads is to associate them with the respective Brahmanas. Of nearly the same age are the Aitareya, Kauṣītaki and Taittirīya Upanishads, while the remnant date from the time of transition from Vedic to Classical Sanskrit.
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